A practical mixed Mode II/III fatigue test rig

3D shear-mode fatigue crack growth in maraging steel and Ti-6Al-4V

“…The asymmetry is such that only a shear force and no bending moment are applied in the cracked section, so that mode I or compressive normal stresses are absent. The device is the same as that described in detail by Hellier et al (1987).…”

“…210 mm-long specimens-similar in shape to those used by Hellier et al (1987)-with a 32.5 mm long waisted central section (10*10 mm in the thinnest part, 15*15 mm in the current section) and a 3.5 mmdeep transverse edge notch in the middle plane were machined. The central area was mechanically polished to allow observations of the crack.…”

“…However, to the authors knowledge, only Hellier et al (1987); Hellier et al (1991Hellier et al ( , 1990; ; Murakami et al (2003Murakami et al ( , 2008 and Pokluda et al (2008); Holáň et al (2009) tried to obtain such mixed-mode data or at least, as concerns Murakami et al, mode II and mode III data on the same material for a comparison. Pokluda et al (2008); Holáň et al (2009) developed a device to obtain the whole range of mode mixity along two parallel, initially circular, crack fronts in austenitic steel cylindrical specimens submitted to transverse shear.…”

“…The final aspect ratio was smaller than predicted under the assumption of similar kinetics and thresholds for mode II and mode III (crack growth was slower at the point where mode III prevailed), which they attributed to a higher shielding of mode III by crack face friction, based on finite element computations of K effective II and K effective III . Hellier et al (1987) developed an asymmetrical 4 points bending device in which a square-section specimen with an edge notch can be turned around a horizontal axis so as to vary continuously K II /K III from zero to infinity. In fact, 3D finite element computations reported below show that pure mode II or III cannot be obtained, except at mid-thickness.…”

On the Mode II Fatigue Threshold for Mild Steel

“…Some were stress-relieved at 550 C for 2 hours and furnace-cooled prior to testing; the majority were left in the asreceived condition. A total of nine such specimens were tested in a four-point shear loading rig previously developed by the first author at The University of New South Wales (Hellier, 1985;Hellier et al, 1987) and shown in Fig. 2.…”